Originally Posted by

**draganicimw** Let's analize triangles ADB and BDC:

- angle DAB = angle BCD

- BD is a common lature

- AB = BC = 5

Rezults from the case of congruence side-side-angle triangle ADB= triangle BDC so angleADB=angleBDC

AB is horizontal and CD is vertical, so if we extend the side AB we'll have a right angle where AB intersect CD (point F). In triangle AFD, F=90 degrees, A=40 degrees, so angleADF = angleADC = 180-90-40 = 50 degrees.

AngleADB is half of angleADC, therefore is 25 degrees.